| Abstrakt: |
The highyield synthesis of the 2,4diaminopyrrolo2,3d pyrimidine 4 PNU87663 viaa Bischlerlike alkylationcyclization sequence was reported earlier. We describe herein an alternative synthesis of this potent antioxidant and several analogs based on the thermal Fischer indolization, starting from hydrazino substituted pyrimidines 5 and 13. In several cases where the thermal Fischer indolization failed, attempts to catalyze the reaction with Lewis acids, especially ytterbium triflate, led to the surprising and unprecedented formation of pyrazolo3,4dpyrimidines, e.g.1methyl3phenyl4,6di1pyrrolidinyl1Hpyrazolo3,4dpyrimidine 24, with the loss of the elements of methane. Mechanistic details of this transformation remain to be investigated. |
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